An organic electroluminescence device (hereinafter, occasionally abbreviated as an organic EL device) using an organic substance is a promising component of a solid-emitting-type full-color display device of a low cost and a large area. Accordingly, various developments of the organic EL device have been made. Typically, an organic EL device is provided with an emitting layer and a pair of opposing electrodes between which the emitting layer is interposed. When an electrical field is applied to the opposing electrodes of the organic EL device, electrons are injected from a cathode and holes are injected from an anode. Further, the injected electrons and holes are recombined with the holes in the emitting layer to form excitons. Energy generated when the excitons are returned from an excited state to a ground state is irradiated as light. The organic EL device emits light in accordance with such a principle.
A typical organic EL device exhibits a higher drive voltage and lower luminescence intensity and lower luminous efficiency than those of an inorganic light-emitting diode. Moreover, since properties of the organic EL device are considerably deteriorated, the organic EL device is not in practical use. Although the organic EL device has been gradually improved in recent years, further higher luminous efficiency, longer lifetime, improvement in color reproduction and the like have been demanded.
Performance of the organic EL device has been gradually enhanced by improving an organic-EL luminescent material. In particular, improvement in color purity of a blue-emitting organic EL device (i.e., shifting emission wavelength into short wavelength) is an important technique leading to improvement in color reproduction of a display.
Patent Literature 1 discloses a luminescent material having dibenzofuran as an example of a material used in an emitting layer. Although blue emission (i.e., emission in short wavelength) is obtained, further improvement has been demanded in view of a low luminous efficiency.
Patent literatures 4 and 5 disclose a diaminopyrene derivative. Patent Literature 2 discloses a combination of an anthracene host and arylamine. Patent Literatures 3 to 5 disclose a combination of an anthracene host having a specific structure and a diaminopyrene dopant. Patent Literatures 6 to 8 disclose an anthracene host material.
Improvement in luminescence property is recognized in any materials and any combinations, but is not sufficient. A luminescent material exhibiting a high luminous efficiency and realizing short-wavelength emission has been demanded.
Patent Literature 9 discloses that an aromatic amine derivative including an arylene group at the center and a dibenzofuran ring bonded to a nitrogen atom is used as a hole transporting material. Patent Literature 10 discloses a use of an aromatic amine derivative as a hole transporting material, in which a dibenzofuran ring, dibenzothiophene ring, benzofuran ring, benzothiophene ring or the like is bonded to a nitrogen atom through an arylene group. However, Patent Literature 10 does not disclose a use of the aromatic amine derivative as a luminescent material.
Patent Literatures 11 to 13 disclose an aromatic amine derivative in which amino groups are respectively bonded to positions 1 and 6 of pyrene. In the aromatic amine derivatives of Patent Literatures 11 and 12, a dibenzofuran ring or a dibenzothiophene ring is bonded to a nitrogen atom of the amino group. Although these aromatic amine derivatives are used as a blue-emitting luminescent material, color purity and luminous efficiency need to be further improved for practical use.